Generally, in order to manufacture a semiconductor integrated circuit, various single wafer processes such as a film forming process, an etching process, a heat treating process, a quality modification process and a crystallization process are repeatedly performed on a target object, e.g., a semiconductor wafer or the like. As a consequence, a required integrated circuit is formed. While executing such processes, processing gases needed for the corresponding processes, e.g., a film formation gas for the film forming process; ozone gas or the like for the quality modification process; O2 gas, an inert gas such as N2 gas, or the like for the crystallization process, are respectively introduced into a processing chamber. For example, in a single wafer processing apparatus for performing heat treatment on semiconductor wafers one by one, a mounting table incorporating therein, e.g., a resistance heater, is installed in a vacuum evacuable processing chamber. Next, a predetermined processing gas is introduced into the processing chamber after mounting a semiconductor wafer on the mounting table to apply various heat treatments on the wafer under predetermined process conditions (see, Japanese Patent Laid-open Applications No. S63-278322, No. H07-078766, No. H06-260430 and No. 2004-356624).
A mounting table structure for mounting thereon a wafer in a processing chamber is generally manufactured by thermally bonding a mounting table together with a supporting column through, e.g., thermal diffusion bond technique. The mounting table is formed by embedding a resistance heater as a heating element in a ceramic material such as AlN or the like and then sintering them as a unit at a high temperature to ensure heat-resistance and corrosion-resistance and preventing metal contamination. The supporting column is also formed by sintering a ceramic material or the like in another process. The mounting table structure formed as a unit with the supporting column stands on a bottom portion of the processing chamber.
In a mounting table made of quartz glass, a resistance heater is embedded between two quartz glass plates and, then, they are press-welded at a high temperature, thereby forming a mounting table where the heater is embedded. Next, a column made of quartz glass is press-welded on a backside of the mounting table at a high temperature to thereby have the mounting table structure to be manufactured.
In the mounting table made of quartz glass, the arrangement pattern of the resistance heater is directly reflected as heat rays on the backside of the wafer due to the comparative transparency of the quartz glass, so that the in-plane temperature uniformity in the wafer may deteriorate. Generally, in order to prevent the deterioration of the in-plane temperature uniformity in the wafer, a thin board-shaped opaque heat-equalizing plate made of a ceramic plate such as SiC, AlN or the like is mounted on the top surface of the mounting table. The wafer is directly mounted on the top surface of the heat-equalizing plate, and then is heated thereon.
However, when the heat-equalizing plate is installed on the mounting table, it is not possible to prevent a processing gas from flowing into a narrow gap formed between a top surface of the mounting table and a bottom surface of the heat-equalizing plate during the treatment of the wafer. Especially when a film forming process is performed, a film forming gas flows into the narrow gap and, hence, an unnecessary attachment film causing particles is deposited thereon. The presence of the unnecessary attachment film causes radiant heat of the heat-equalizing plate to be changed, thereby deteriorating the in-plane temperature uniformity in the wafer.
Moreover, since the wafer is mounted on the mounting table via the heat-equalizing plate, contact heat resistance between solid surfaces lowers thermal conductivity. That is, the heating efficiency of the wafer is decreased. Furthermore, in the above mounting table structure, the mounting table cannot serve as a lower electrode, so that a high frequency power cannot be applied even if the high frequency needs to be supplied to perform the plasma processing.